gplepage/vegas: vegas version 5.2

Introduces new implementation for using multiple processors to evaluate expensive integrands. The new implementation is simpler than using MPI (which is still supported) and is based on Python's standard multiprocessing library (so, unlike MPI, does not require additional software beyond what comes standard with Python). New keyword nproc specifies the number of processes/processors that are used in parallel to evaluate the integrand. Assumes Python 3.3 or later.

Multiple processors are also supported for PDFIntegrator and for AdaptiveMap.adapt_to_samples.

New setup.py forces Cython to rebuild *.c files when using Python 3.11 or later. This addresses incompatibilities introduced by 3.11.